I'm not looking for apps built in hackathons - but examples of open data used in real business, or even better businesses built around open data itself (commercial entities that make money, not non profits)

Do you know of any such examples or books/websites where I can find them?

The Open Data 500 is a collection of 500 companies that have built a business model on open data (both government and non-government data). Note that the Open Data 500 is expanding to include other countries as well.

Highlights on Data.gov show companies, civil society groups, non-profits, and citizens using open government data

... Often, the free data isn't their only source, but used to narrow things down; the folks drilling for oil may use NOAA or NASA earth-observing data to find candidate areas, and then do their own data collection to determine if the area's good or not.

There are millions of examples of Open Data being used to support business. A more interesting business model around data are companies that resell data aggregated from multiple open sources into one consistent dataset they then turn into a commodity. Two that come to mind are Platts Energy and Ventus Energy who sell datasets (transmission lines, substations, etc) as products either as a subscription or as a bulk download with terms of use and restrictions on redistribution. I'd imagine many of these types of companies exist by selling governments back their data cleaned up and QA/QC to employees ignorant about what open data exists or to lazy time pressed to do the data cleaning/review themselves

Well, my advice would be just look around. An increasingly large number of companies are making use of open data. A number of products and services around us are based on open data.

Ever since UK’s Open Data Institute came up in 2012, a large number of UK companies have turned towards open data for churning out their strategies and products. You can click here to read more about it.

Therefore, it’s difficult to pinpoint in the direction of any one source.
Instead, I will share a couple of examples of how businesses are making use of open data in business.

Take the case of an entrepreneurial venture like Magpie Supply. Magpie supply enabled state farmers to locate the under-utilized truck space to reduce the cost of transportation. They also provide a platform to access historic farmers’ market prices on a map. This helps agriculturalists to identify new markets for selling opportunities.

Similarly a company like Red Roof Inn is making creative use of open data regarding weather conditions to create value for its customers.
It processes the information about weather conditions, flight cancellations and customers’ locations and comes up with recommendations regarding last-minute hotel deals to stranded travelers.
It has developed an algorithm that takes into account travel conditions in order to work out details about availability of nearby hotels and rates. This helps the stranded travelers in a big way.

We're a data company that caters to Sales Tech and HR Tech companies. Though we do not offer open data [we have released an open source dataset recently] we do offer clean, enriched data from our dataset. You can read some of our case studies on our website, where companies including Workable have utilized our data to increase platform performance, generate more leads, and qualify incoming traffic.